Positronium yields in liquids determined by lifetime and angular correlation measurements

Abstract

Positron lifetime and angular correlation spectra were measured for 36 pure liquids, CCl 4 mixtures with hexane and diethylether, and C 6F 6 mixtures with hexane. Apparent ortho-Ps yields, I' 3, were determined as the intensity of the long-lived component in the lifetime spectra, while the apparent para-Ps yields, I' 3, were obtained as the intensity of the narrowest gaussian in a three-gaussian fit to the angular correlation spectra. The ratio I' 3/ I 1, expected to be 3, was found to be instead 2.3 (average value for 3 ethers), 2.5 (average value for 10 linear, branched, and cyclic aliphatic hydrocarbons), 3.2 (average value for 8 aromatic hydrocarbons), 2.6 (average value for 5 alcohols). Values of this ratio for various other liquids are also given. The results for the mixtures show how I' 3 and I' 1, vary as the Ps formation is inhibited (CCl 4 mixtures) or enhanced C 6F 6 mixtures). The most important experimental result, namely that I ' 3/ I 1 < 3 for many liquids, is discussed in detail. Although it cannot be excluded that this effect is caused by the special model (3 gaussians) used to determine I 1, there are good reasons to believe the effect is real. In this case the cause might be secondary Ps reactions with other reactants in the positron spur (e.g. Ps − formation, conversion on free radicals, and Ps or Ps − oxidation by positive ions) or various processes influencing the Ps formation.